Digital I/O

cancel
Showing results for 
Search instead for 
Did you mean: 

Input impedance of NI 9422 digital input module

Hi,

 

I  want to know what is the input impedance of the NI 9422 module. I'm using the module with a proximity sensor to detect the position of a moving part.

 

Here's the setup I'm using:

 

I have a 10k pullup resistor between 24VDC and DI+ pin, the proximity sensor is in parrallel with DI+ and DI- with DI- hooked up to ground.

 

When the proximity sensor is ON the voltage between DI+ and DI- is 0.8 VDC wich is the VCE voltage of the internal transistor inside the proximity switch, this is fine. But when the proximity sensor is OFF the voltage reading is 6.8VDC. Supposed the circuit is a voltage devider with my pullup and the internal resistor, I figure the internal impedance is about 3.8k, is that right ???

 

Thanks

0 Kudos
Message 1 of 2
(3,202 Views)

Hi MikeLaw.

 

The datasheet does not include this information because impedance is a strong function of voltage. This KB explains all.

 

Hope this helps,

Regards, 

Kind Regards
James Hillman
Applications Engineer 2008 to 2009 National Instruments UK & Ireland
Loughborough University UK - 2006 to 2011
Remember Kudos those who help! 😉
0 Kudos
Message 2 of 2
(3,187 Views)